package Q3;

import java.util.LinkedList;
import java.util.Queue;
import java.util.Scanner;

public class Main {

    public static int ret;
    public static int n; //B 横坐标
    public static int m; //B 纵坐标
    public static int x; //马横坐标
    public static int y; //马纵坐标
    public static boolean[][] flag;

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        n = scanner.nextInt();
        m = scanner.nextInt();
        x = scanner.nextInt();
        y = scanner.nextInt();

        flag = new boolean[n][m];

        dfs(0, 0);

        System.out.println(ret);

    }

    /**
     *
     * @param a 当前横坐标
     * @param b 当前纵坐标
     */
    public static void dfs(int a, int b) {
        if (a == n - 1 && b == m - 1) {
            ret++;
            return;
        }

        if (a >= n || b >= m || (a == x && b == y) || Math.abs(a - x) + Math.abs(b - y) == 3) {
            return;
        }

//        flag[a][b] = true;

        //向右走
        dfs(a, b + 1);

        //向下走
        dfs(a + 1, b);

//        flag[a][b] = false;
    }
}
